Plant nutrients can be classified as primary plant nutrients (sources of nitrogen, phosphorus and potassium); secondary plant nutrients (sources of calcium, magnesium and sulfur); and micronutrients (such as copper, zinc, boron, iron, manganese, molybdenum and the like). Such nutrients are often made available for sale in the form of water-soluble granular fertilizers. The granular fertilizers can be dissolved in water and delivered to plants for uptake, such as occurs in greenhouse operations. Alternatively, they can be broadcast over a field, in which event, they will solubilize over time by exposure to rainfall and other precipitation, for uptake by nearby crops.
As is well known in the art, many granular fertilizers, and particularly those containing relatively high levels of the secondary plant nutrients calcium and/or magnesium, have a tendency to cake and clump when stored for any significant period of time. If this occurs, and the material is intended for broadcast spreading, it is necessary for the user to crush or otherwise break up the material prior to use. Even if the material is intended for dissolution, it is commonplace for a preparatory crushing operation to be employed, to speed solubilization. This is inconvenient, and can require users to possess crushing equipment.
To avoid the need for preparatory crushing operations, it is known for fertilizer manufacturers to provide the fertilizer in a two-part form, to enhance storage-stability.
For example, it is known for fertilizer manufacturers to provide a fertilizer first part, composed largely of primary plant nutrients and micronutrients, and a fertilizer second part, composed largely of secondary plant nutrients containing calcium and/or magnesium. Sometimes the first part and the second part are vended in separate bags, for mixing shortly prior to use. This “two-bag system” avoids the potential for clumping, since the calcium and/or magnesium compounds of the second part are isolated from the phosphorus-containing first part until use. However, this system increases the likelihood of misapplication. It is also known to package the second part in a bag which itself is contained in a bag which holds the first part. This “bag-in-bag system” renders misapplication relatively unlikely. However, this latter system is relatively inconvenient to use, since the user must open the outer bag; find, remove and open the inner bag; and mix the contents of the bags together prior to use. Additionally, production of bag-in-bag systems of the prior art is relatively labour intensive.